Non-oriented electrical steel sheet, motor including same, and method for manufacturing non-oriented electrical steel sheet

Abstract

The present invention relates to a non-oriented electrical steel sheet comprising, in weight% (wt%), 0.1 to 1.6% of silicon (Si), 0.5% or less (more than 0) of aluminum (Al), 0.2 to 0.4% of manganese (Mn), 0.0050% or less (more than 0) of carbon (C), 0.0050% or less (more than 0) of sulfur (S), 0.0030% or less (more than 0) of nitrogen (N), 0.0050% or less (more than 0) of titanium (Ti), 0.1% or less (more than 0) of phosphorus (P), and the balance of iron (Fe) and other inevitable impurities, wherein the volume fraction of TiC precipitates having an average diameter of 200 nm or less in the non-oriented electrical steel sheet is 20% or less, and the volume fraction of MnS precipitates having an average diameter of 200nm or less in the non-oriented electrical steel sheet is 20% or less.

Description

Non-oriented electrical steel sheet, motor including the same, and method for manufacturing non-oriented electrical steel sheet

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same.

[0002] A motor generates mechanical energy by using electrical energy as the driving force to rotate an internal iron core. The internal iron core is formed by stacking multiple sheets of non-oriented electrical steel that have been punched into the shapes of a stator and a rotor; in this process, the magnetic properties of the non-oriented electrical steel have a dominant influence on the performance of the motor (or motor core).

[0003] The magnetic properties of non-oriented electrical steel are evaluated by magnetic flux density and iron loss. Magnetic flux density is related to the motor's torque, while iron loss is the amount of energy lost as heat.

[0004] To increase the energy efficiency of motors, the iron loss of non-oriented electrical steel sheets must be reduced. This can be achieved by adding major alloying elements such as silicon (Si), manganese (Mn), and aluminum (Al) to increase resistivity, thinning the material, or controlling the grain size and precipitate size through heat treatment. However, major alloying elements readily combine with impurity elements such as carbon (C), sulfur (S), nitrogen (N), and titanium (Ti) to form precipitates. These formed precipitates hinder the movement of magnetic domains formed by an applied magnetic field, thereby degrading magnetic properties and reducing rollability, which can make it difficult to thin the steel sheet.

[0005] Therefore, research on managing precipitates in non-oriented electrical steel sheets is actively underway.

[0006] The present invention aims to solve various problems, including the aforementioned problems, and provides a non-oriented electrical steel sheet with reduced precipitate formation through temperature range control during the manufacturing process, a motor including the same, and a method for manufacturing the non-oriented electrical steel sheet.

[0007] However, these tasks are exemplary and do not limit the scope of the invention.

[0008] According to one aspect of the present invention, a non-oriented electrical steel sheet is provided, comprising, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities, wherein the volume fraction of TiC precipitates with an average diameter of 200 nm or less within the non-oriented electrical steel sheet is 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less is 20% or less.

[0009] In one embodiment, the iron loss (W of the non-oriented electrical steel sheet) 15 / 50 ) may be 7.0W / kg or less.

[0010] In one embodiment, the magnetic flux density (B) of the non-oriented electrical steel sheet 50 ) can be 1.75T or more.

[0011] In one embodiment, the grain size of the final microstructure may be 50 μm to 160 μm.

[0012] In one embodiment, the tensile strength (TS) of the non-oriented electrical steel sheet may be 500 MPa or more, and the yield strength (YP) may be 400 MPa or more.

[0013] According to one aspect of the present invention, a method for manufacturing a non-oriented electrical steel sheet comprises: a continuous casting step of forming a slab comprising, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities; a hot rolling step of manufacturing a hot-rolled sheet by reheating the slab and then hot-rolling and coiling it; and a cold rolling step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet. The present invention provides a method for manufacturing a non-oriented electrical steel sheet, comprising a cold rolling annealing step of annealing the cold rolled sheet to produce a cold rolled annealed sheet, wherein the coiling temperature in the hot rolling step is performed at less than 600℃, and the volume fraction of MnS precipitates with an average diameter of 200nm or less in the final microstructure is 20% or less.

[0014] In one embodiment, the slab temperature can be maintained at 800°C or higher between the continuous casting step and the reheating.

[0015] In one embodiment, in the hot rolling step, the reheating temperature range may be performed at 800°C or higher.

[0016] In one embodiment, in the hot rolling step, the finishing rolling temperature range may be performed at 800°C or higher.

[0017] In one embodiment, the volume fraction of TiC precipitates with an average diameter of 200 nm or less in the final microstructure may be 20% or less.

[0018] In one embodiment, the grain size of the final microstructure may be 50 μm to 160 μm.

[0019] In one embodiment, the iron loss (W of the non-oriented electrical steel sheet)15 / 50 ) may be 7.0W / kg or less.

[0020] In one embodiment, the magnetic flux density (B) of the non-oriented electrical steel sheet 50 ) can be 1.75T or more.

[0021] In one embodiment, the tensile strength (TS) of the non-oriented electrical steel sheet may be 500 MPa or more, and the yield strength (YP) may be 400 MPa or more.

[0022] According to one aspect of the present invention, a motor is provided comprising a motor core, wherein the motor core comprises, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), the remainder being iron (Fe) and unavoidable impurities, wherein the volume fraction of TiC precipitates with an average diameter of 200 nm or less within the non-oriented electrical steel sheet is 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less is 20% or less.

[0023] In one embodiment, the iron loss (W of the non-oriented electrical steel sheet) 15 / 50 ) may be 7.0W / kg or less.

[0024] In one embodiment, the magnetic flux density (B) of the non-oriented electrical steel sheet 50 ) can be 1.75T or more.

[0025] Other aspects, features, and advantages other than those described above will become clear from the following specific details, claims, and drawings for implementing the invention.

[0026] According to one embodiment of the present invention as described above, a non-oriented electrical steel sheet having low surface roughness and a thin coating film to ensure insulation, while simultaneously having low iron loss and high magnetic flux density to produce a motor with a high packing factor, a motor including the same, and a method for manufacturing the same can be provided. Of course, the scope of the present invention is not limited by these effects.

[0027] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0028] FIG. 2 is a temperature graph schematically illustrating a part of a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0029] Figure 3 is a temperature graph schematically illustrating a part of the method for manufacturing a non-oriented electrical steel sheet according to a comparative example of the present invention.

[0030] The present invention will be described in detail below. However, in describing the present invention, if it is determined that a detailed description of related known technologies or configurations may unnecessarily obscure the essence of the present invention, such detailed description will be omitted.

[0031] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0032] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0033] In the following embodiments, when various components such as layers, films, regions, and plates are described as being "on" another component, this includes not only cases where they are "directly on" another component, but also cases where another component is interposed between them.

[0034] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated.

[0035] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0036] In this specification, "A and / or B" indicates the case where it is A, B, or both A and B. Additionally, in this specification, "at least one of A and B" indicates the case where it is A, B, or both A and B.

[0037] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0038] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0039] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. FIG. 2 is a temperature graph schematically illustrating a part of the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. FIG. 3 is a temperature graph schematically illustrating a part of the method for manufacturing a non-oriented electrical steel sheet according to a comparative example of the present invention.

[0040] Referring to FIG. 1, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may include a continuous casting step (S10), a hot rolling step (S100), a preliminary annealing step (S200), a cold rolling step (S300), a cold rolling annealing step (S400), and a coating step (S500).

[0041] Continuous casting step (S10)

[0042] In a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, the semi-finished product subject to hot rolling may be a slab. The slab in the semi-finished product state can be obtained through a continuous casting process after obtaining molten steel of a predetermined composition through a steelmaking process.

[0043] First, the slab can be manufactured through a continuous casting process. The slab may contain silicon (Si), manganese (Mn), aluminum (Al), the remainder being iron (Fe), and unavoidable impurities. Additionally, the slab may further contain carbon (C), sulfur (S), nitrogen (N), and titanium (Ti). In this case, carbon (C), sulfur (S), nitrogen (N), and titanium (Ti) may correspond to impurity elements.

[0044] In one embodiment, the slab may contain, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities.

[0045] The following explains the reason why the numerical range of components included in non-oriented electrical steel sheets is limited.

[0046] Carbon (C)

[0047] Since carbon can increase iron loss by forming carbides such as TiC and NbC, it must be contained in an appropriate amount in the slab. The carbon content in the slab may be 0.0050 weight% or less (greater than 0). If the carbon content in the slab exceeds 0.0050 weight%, magnetic aging may occur, which may degrade magnetic properties.

[0048] Silicon (Si)

[0049] Silicon is a major additive element that can lower iron loss by increasing resistivity. The silicon content in the slab may be 0.1 wt% to 1.6 wt%. If the silicon content in the slab is less than 0.1 wt%, it may be difficult to obtain a sufficient iron loss improvement effect. If the silicon content in the slab exceeds 1.6 wt%, the brittleness of the material increases, which may cause plate breakage during coiling and cold rolling, resulting in a sharp decrease in rolling productivity and a decline in punchability, which may increase the difficulty of the production process. In addition, permeability and magnetic flux density may decrease.

[0050] Manganese (Mn)

[0051] Manganese, together with silicon, can increase resistivity, thereby lowering iron loss and improving texture. The manganese content in the slab may be 0.2 wt% to 0.4 wt%. If the manganese content in the slab is less than 0.2 wt%, fine MnS precipitates may form, inhibiting grain growth and potentially degrading magnetic properties such as reduced magnetic flux density. If the manganese content in the slab exceeds 0.4 wt%, excessive precipitation of MnS may occur, promoting the formation of a texture unfavorable to magnetism, which may lead to a rapid decrease in magnetic flux density and a decrease in cold rolling performance.

[0052] Aluminum (Al)

[0053] Aluminum can increase resistivity together with silicon to lower iron loss. Aluminum can combine with nitrogen to form AlN precipitates. The aluminum content in the slab may be 0.5 weight% or less (greater than 0). If the aluminum content in the slab exceeds 0.5 weight%, a decrease in cold rolling performance may occur, and AlN may form on the surface during cold rolling annealing, which increases iron loss and decreases magnetic flux density, thereby deteriorating magnetic properties.

[0054] Yellow (S)

[0055] Sulfur forms precipitates such as MnS and CuS, which inhibit grain growth and increase iron loss, so it is desirable to add it in low amounts. The sulfur content in the slab may be 0.0050 wt% or less (greater than 0). If the sulfur content in the slab exceeds 0.0050 wt%, magnetic properties may deteriorate due to increased sulfide formation.

[0056] Nitrogen (N)

[0057] Nitrogen combines with Al, Ti, Nb, etc. to form precipitates such as AiN, TiN, and NbN, which inhibit grain growth and increase iron loss; therefore, it is desirable to add it in low amounts. The nitrogen content in the slab may be 0.0030 wt% or less (greater than 0). If the nitrogen content in the slab exceeds 0.0030 wt%, magnetic properties may deteriorate due to increased nitride formation.

[0058] Titanium (Ti)

[0059] Titanium is an element with a very strong tendency to form precipitates in steel. It combines with C and N to form fine precipitates such as TiC and TiN, which inhibit grain growth and increase iron loss; therefore, it is desirable to add it in low amounts. The titanium content in the slab may be 0.0050 wt% or less (greater than 0). If the titanium content in the slab exceeds 0.0050 wt%, magnetic properties may deteriorate due to increased formation of carbides and nitrides.

[0060] Ph(P)

[0061] Phosphorus is a grain boundary segregation element that develops texture. The phosphorus content in the slab may be 0.01 weight% or less (greater than 0). If the phosphorus content in the slab exceeds 0.01 weight%, the segregation effect may inhibit grain growth, deteriorate magnetic properties, and reduce cold rolling performance.

[0062] It will be understood by anyone with ordinary knowledge in the technical field to which this invention pertains that, in addition to the components described above, various components included in non-oriented electrical steel sheets may be included as components of the non-oriented electrical steel sheet of this invention. Combinations of commonly known components and their applications naturally fall within the scope of the rights of this invention.

[0063] Hot rolling step (S100)

[0064] In the hot rolling step (S100), the above-mentioned slab can be hot-rolled to produce a hot-rolled plate.

[0065] Referring to FIG. 2, the hot rolling step (S100) may include a step of reheating the slab (S110), a step of rolling the reheated slab (S120), and a step of winding the rolled slab (S130).

[0066] First, the slab manufactured including the above components may undergo a cooling step (i.e., a first cooling step) before reheating after continuous casting. The cooling step of the slab may be an air cooling or a ventilation cooling step. At this time, the starting temperature for reheating the slab may be set to avoid the TiC precipitate formation temperature range of 700°C to 800°C. Therefore, after continuous casting, the slab may be stored and maintained at a temperature higher than 800°C.

[0067] In the hot rolling step (S100), the slab may be reheated. If the slab reheating temperature (SRT) is too high, precipitates such as carbon (C), sulfur (S), and nitrogen (N) within the slab (e.g., AlN) may be redissolved, and fine precipitates may be formed during subsequent rolling and annealing steps, which may inhibit grain growth and degrade magnetic properties. If the slab reheating temperature is too low, the rolling load increases during hot rolling, which may reduce rollability. In one embodiment, the starting temperature for slab reheating in the hot rolling step (S100) is greater than 800°C, and the slab reheating temperature may be between 1,050°C and 1,250°C.

[0068] After reheating the slab, the heated slab can be rolled at a predetermined finishing delivery temperature (FDT). The finishing delivery temperature of the hot rolling step (S100) may be 800°C to 1,000°C. When rolling at the finishing delivery temperature, material variation of the electrical steel sheet is prevented, and an electrical steel sheet with excellent mechanical and magnetic properties can be manufactured.

[0069] After rolling the slab at a predetermined finishing rolling temperature, it can be cooled to a predetermined coiling temperature (CT) and coiled. According to one embodiment, the coiling temperature may be less than 600°C, more specifically 450°C or higher and less than 600°C. If the coiling temperature is less than 450°C, the brittleness of the steel plate increases, and plate breakage may occur during coiling. If the coiling temperature is 600°C or higher, fine AlN may be formed during cooling after coiling, which may increase iron loss.

[0070] As described above, in the hot rolling step (S100), the reheating temperature and the finishing rolling temperature may be performed at 800°C or higher. Additionally, the coiling temperature may be performed at a condition lower than 600°C. This temperature design can be understood as an attempt to avoid the temperature range (Tf) in which fine precipitates with an average diameter of 200 nm or less (hereinafter referred to as 'fine precipitates') are formed during the reheating, rolling, and coiling processes. For example, the fine precipitates may include TiC and MnS, etc.

[0071] The above-mentioned fine precipitates can act as a factor affecting the magnetic properties of non-oriented electrical steel sheets. In particular, precipitates with an average diameter of 200 nm or less, more specifically 20 nm to 200 nm, have a size similar to that of the magnetic domain walls within the grains. Consequently, they can impede magnetization through a pinning effect during steel sheet magnetization, thereby causing high iron loss and low magnetic flux density, which can degrade the magnetic properties of non-oriented electrical steel sheets.

[0072] In one embodiment, the temperature range for forming TiC precipitates may be 700°C to 800°C. The step of reheating the slab (S110) and the step of rolling the reheated slab (S120) may be performed by avoiding the temperature range. In the step of hot rolling the slab (S100), the slab reheating temperature may be 1,050°C to 1,250°C, and the finishing rolling temperature may be 800°C to 900°C.

[0073] In one embodiment, the temperature range for forming MnS precipitates may be 650°C to 1,050°C. The temperature range for forming MnS precipitates may have a somewhat wider temperature range compared to TiC. In this case, MnS precipitates may exhibit a tendency to precipitate in finer sizes as the temperature decreases. More specifically, for MnS precipitating at low temperatures, such as 800°C or lower, particularly around 650°C, the precipitation driving force is not large, so a large number of fine precipitates with an average particle size of 200 nm or less may be formed among the MnS precipitates. Therefore, the step of winding the rolled slab (S130) may be performed by avoiding the above temperature range. In the step of winding the rolled slab (S130), the winding temperature may be less than 600°C, more specifically, between 500°C and 600°C.

[0074] A cooling step (i.e., a second cooling step) may be included between the step of rolling the reheated slab (S120) and the step of coiling the rolled slab (S130). Specifically, the step of cooling the rolled slab may refer to the range between the finishing rolling temperature and the temperature at which coiling begins. As described above, the finishing rolling temperature may be performed at 800°C or higher, and the coiling temperature may be performed at less than 600°C. The rolled slab may be cooled from the finishing rolling temperature to the coiling start temperature, and at this time, to quickly avoid the fine precipitate formation temperature range (Tf), it may be cooled at an average cooling rate of 50°C / s or higher and 200°C / s or lower. In this way, by quickly avoiding the fine precipitate formation temperature range (Tf) and reducing the residence time at that temperature, the formation of fine precipitates can be effectively suppressed. The cooling method is not particularly limited, and any method such as water cooling, oil cooling, or air cooling can be used alone or in combination.

[0075] Referring to FIG. 3 as a comparative example, during the cooling process after continuous casting, the slab can be cooled to 600°C or lower, for example, to 100°C or lower. There are no restrictions on the cooling method, but the cooling may be performed by air cooling by leaving the slab at room temperature. Subsequently, the slab undergoes a hot rolling process, during which the slab can be reheated to a temperature of approximately 1200°C. During this reheating process, the slab inevitably passes through the fine precipitate formation temperature range (Tf). More specifically, the slab according to the comparative example passes through the fine precipitate formation temperature range (Tf) twice: once during the cooling process after continuous casting and again during the slab reheating process. Furthermore, as the coiling temperature during the coiling stage after hot rolling is 600°C or higher, i.e., within the fine precipitate formation temperature range (Tf), fine precipitates are formed even more excessively.

[0076] On the other hand, in the non-oriented electrical steel sheet according to one embodiment of the present invention described above, the slab temperature is maintained at 800°C or higher during the cooling process after continuous casting of the slab, the finish rolling temperature is set at 800°C or higher, and the cooling section from the finish rolling temperature to the coiling start temperature is rapidly avoided so that the coiling temperature is performed at 600°C or lower, thereby avoiding the temperature range (Tf) for the formation of fine precipitates. Accordingly, by effectively suppressing the formation of fine precipitates with an average diameter of 200 nm or less that degrade the magnetic properties of the non-oriented electrical steel sheet, it is possible to manufacture a non-oriented electrical steel sheet having excellent magnetic properties.

[0077] In one embodiment of the present invention, the thickness of the hot-rolled plate after hot rolling may be 1.8 mm to 2.6 mm. At this time, if the thickness of the hot-rolled plate exceeds 2.6 mm, the cold rolling reduction rate increases, so the texture of the final product may deteriorate.

[0078] Preliminary annealing step (S200)

[0079] A preliminary annealing step (S200) may be performed after the hot rolling step (S100). However, the present invention is not limited thereto. The preliminary annealing step (S200) may be omitted. In this case, a cold rolling step (S300) may be performed after the hot rolling step (S100).

[0080] In the preliminary annealing step (S200), a pre-annealed plate can be manufactured by hot-rolling and annealing a coiled and cooled hot-rolled plate.

[0081] The preliminary annealing step (S200) may include the steps of raising the temperature of the hot-rolled plate to a predetermined annealing temperature, annealing at a predetermined annealing temperature, cooling the annealed hot-rolled plate, and performing shot blasting and pickling. Through the preliminary annealing step (S200), the uniformity of the microstructure and cold rolling performance of the hot-rolled plate can be ensured.

[0082] In the pre-annealing step (S200), the hot-rolled plate can be heated (or heated) to the pre-annealing temperature at a heating rate of 5℃ / s to 30℃ / s. At this time, if the heating rate is less than 5℃ / s, productivity may decrease and the manufacturing cost may increase. On the other hand, if the heating rate exceeds 30℃ / s, non-uniform grain growth may occur, which may result in a decrease in the magnetic properties of the final product.

[0083] In the preliminary annealing step (S200), the hot-rolled plate heated at the aforementioned heating rate can be annealed at an annealing temperature of 900°C to 1,100°C for a period of 30 to 120 seconds. At this time, if the annealing temperature of the preliminary annealing step (S200) is too low, the elongated cast structure after hot rolling remains, causing microstructural non-uniformity and forming small grains, which may reduce cold rolling performance. On the other hand, if the annealing temperature of the preliminary annealing step (S200) is too high, the grains grow excessively, the grain size variation increases, and an imbalance in the texture of the final product may occur, and anisotropy may develop.

[0084] In the preliminary annealing step (S200), the hot-rolled plate, which has been heated at the above-mentioned heating rate and then annealed at the above-mentioned annealing temperature, can be cooled at a cooling rate of 30℃ / s or more and 50℃ / s or less. If the cooling rate is less than 30℃ / s, productivity may decrease and the manufacturing cost may increase. On the other hand, if the cooling rate exceeds 50℃ / s, thermal stress may accumulate inside the hot-rolled plate during the cooling process, increasing the likelihood of plate breakage during cold rolling.

[0085] After heating, annealing, and cooling the hot-rolled plate in the preliminary annealing step (S200), the hot-rolled plate may undergo a shot blast process before cold rolling. The shot blast process is a process of removing scale formed on the surface of the hot-rolled plate by applying physical force to the hot-rolled plate; more specifically, metal grit may be sprayed onto the surface of the hot-rolled plate to destroy and remove the scale formed on the surface of the hot-rolled plate after hot rolling.

[0086] A pickling process may be additionally performed after the shot blasting process. In the pickling process, the oxide layer formed on the surface of the hot-rolled plate can be removed using a pickling solution.

[0087] Cold rolling step (S300)

[0088] A cold rolling step (S300) may be performed after a preliminary annealing step (S200). In the cold rolling step (S300), a pre-annealed plate that has been hot-rolled and annealed may be cold-rolled to produce a cold-rolled plate. In the cold rolling step (S300), the pre-annealed plate may be cold-rolled to a thickness of 0.7 mm or less, more specifically 0.15 mm to 0.7 mm. In one embodiment, to impart rollability, the plate temperature (e.g., the temperature of the pre-annealed plate) may be raised and hot rolling may be performed.

[0089] The reduction rate in the cold rolling step (S300) may be 25% to 75%. When cold rolling is performed under the above conditions, the mechanical properties and magnetic properties of the final product may be excellent.

[0090] After cold rolling, the cold-rolled grain size may be about 50㎛ to 160㎛.

[0091] Cold rolling annealing stage (S400)

[0092] After the cold rolling step (S300), a cold rolling annealing step (S400) may be performed. At this time, the cold rolling annealing step (S400) may be referred to as the final annealing step. In the cold rolling annealing step (S400), a cold rolling annealed plate may be manufactured by cold rolling annealing the cold rolling plate. The cold rolling annealing step (S400) may be omitted depending on the characteristic requirements of the final product and the step conditions.

[0093] The cold rolling annealing step (S400) can be performed at a temperature that derives the optimal grain size by considering the final magnetic and mechanical properties.

[0094] In one embodiment, the cold rolling annealing step (S400) may include the step of heating the cold rolled plate to an annealing temperature of 850°C to 1,000°C at a heating rate of 10°C / s or more, the step of maintaining it for 5 seconds to 70 seconds, and the step of cooling the annealed cold rolled plate at a cooling rate of 20°C / s or more and 50°C / s or less.

[0095] If the cold rolling annealing temperature in the cold rolling annealing step (S400) is less than 850°C, the grain size is fine, which may increase hysteresis loss and increase the area fraction of a texture unfavorable to magnetism in the final product. On the other hand, if the cold rolling annealing temperature exceeds 1,000°C, the grain size becomes coarse, which may increase eddy current loss. Additionally, if the holding time is less than 5 seconds, grain growth does not occur sufficiently, which may increase hysteresis loss. On the other hand, if the holding time exceeds 70 seconds, productivity decreases, which may increase manufacturing costs.

[0096] The cold rolling annealing step (S400) may be performed in an atmosphere containing a mixed gas to prevent surface oxidation and nitriding. For example, a cold rolling annealing plate with excellent surface condition can be obtained by performing the cold rolling annealing step (S400) in an atmosphere containing a mixed gas consisting of nitrogen and hydrogen. In one embodiment, the cold rolling annealing step (S400) may be performed in an atmosphere containing a gas consisting of hydrogen, nitrogen, and residual oxygen.

[0097] Coating step (S500)

[0098] A coating step (S500) may be performed after the cold-rolled annealing step (S400). In the coating step (S500), a coating layer may be formed on the surface of the cold-rolled annealed plate. The formation of the coating layer may be performed by a method well known to a person skilled in the art. For example, it may be performed by applying or spraying a composition for the coating layer onto one or both sides of the steel plate. By forming a coating layer through the coating step (S500), the stampability of the final product can be improved and insulation properties can be secured.

[0099] As described above, a non-oriented electrical steel sheet can be manufactured by forming a coating layer on the surface of a cold-rolled annealed sheet.

[0100] Non-oriented electrical steel sheets

[0101] A non-oriented electrical steel sheet according to one embodiment of the present invention can be manufactured by the method for manufacturing a non-oriented electrical steel sheet described above.

[0102] The non-oriented electrical steel sheet produced by the above manufacturing method may have a volume fraction of TiC precipitates with an average diameter of 200 nm or less in the final microstructure of 20% or less. Additionally, the non-oriented electrical steel sheet may have a volume fraction of MnS precipitates with an average diameter of 200 nm or less in the final microstructure of 20% or less. Fine precipitates with an average diameter of 200 nm or less may act as a factor affecting the magnetic properties of the non-oriented electrical steel sheet. In particular, precipitates with an average diameter of 200 nm or less, more specifically 20 nm to 200 nm, have a size similar to that of the domain walls within the grains; therefore, they may impede magnetization through a pinning effect during the magnetization of the steel sheet, thereby causing high iron loss and low magnetic flux density, which can degrade the magnetic properties of the non-oriented electrical steel sheet.

[0103] Accordingly, in a non-oriented electrical steel sheet according to one embodiment of the present invention, the volume fraction of TiC precipitates with an average diameter of 200 nm or less in the final microstructure can be limited to 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less can be limited to 20% or less.

[0104] The volume fraction of the above-mentioned fine precipitates can be easily controlled by avoiding the temperature range in which fine precipitates precipitate during the manufacturing process as described above. That is, the slab temperature can be maintained at 800°C or higher before reheating after continuous slab casting, the finish rolling temperature can be set at 800°C or higher, and the coiling temperature can be performed at less than 600°C. By controlling the fraction of fine precipitates contained in the non-oriented electrical steel sheet in this way, a non-oriented electrical steel sheet having excellent iron loss and magnetic flux density can be provided. In one embodiment, the grain size of the non-oriented electrical steel sheet may be 50 µm or more and 160 µm or less.

[0105] In one embodiment, the tensile strength (TS) of the non-oriented electrical steel sheet may be 500 MPa or more, and the yield strength (YP) may be 400 MPa or more.

[0106] In one embodiment, the iron loss (W of a non-oriented electrical steel sheet) 15 / 50 ) may be 7.0 W / kg or less. Specifically, the iron loss (W of non-oriented electrical steel) 15 / 50 ) may be 1.0 W / kg or more and 7.0 W / kg or less.

[0107] In one embodiment, magnetic flux density B of a non-oriented electrical steel sheet 50 It can be 1.75T or more.

[0108] Non-oriented electrical steel sheet and motor including the same

[0109] A motor core manufactured by the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may comprise, in weight % (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities.

[0110] In one embodiment, the non-oriented electrical steel sheet may include a coating layer formed on one or both sides of a base material. Here, the base material may be a steel sheet.

[0111] In one embodiment of the present invention, the volume fraction of TiC precipitates having an average diameter of 20 nm to 500 nm in a non-oriented electrical steel sheet may be 20% or less, and the volume fraction of MnS precipitates having an average diameter of 100 nm or less may be 20% or less. In this way, by controlling the fraction of fine precipitates contained in the non-oriented electrical steel sheet, a non-oriented electrical steel sheet having excellent iron loss and magnetic flux density can be provided.

[0112] A motor according to one embodiment of the present invention may include a motor core, and the motor core may be formed by stamping and laminating non-oriented electrical steel sheets into a predetermined shape. That is, a motor according to one embodiment of the present invention may include such non-oriented electrical steel sheets. In other words, a motor core may be manufactured by laminating such non-oriented electrical steel sheets, and a motor may be manufactured using such a motor core.

[0113] In one embodiment, the packing density of the motor core may be 96% or higher. A motor including a motor core manufactured in this way may have excellent magnetic properties and high efficiency.

[0114]

[0115] Experimental Example

[0116] The present invention will be explained in more detail below through experimental examples. However, the following experimental examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited by the following experimental examples. The following experimental examples may be appropriately modified or changed by those skilled in the art within the scope of the present invention.

[0117] Each example and comparative example was prepared by the following method.

[0118] (1) A slab was produced through a continuous casting process containing, in weight percent, 0.24% silicon (Si), 0.001% aluminum (Al), 0.208% manganese (Mn), 13 ppm carbon (C), 25 ppm sulfur (S), 645 ppm phosphorus (P), 15 ppm nitrogen (N), and 20 ppm titanium (Ti), with the remainder being iron (Fe) and unavoidable impurities.

[0119] (2) The temperature immediately before reheating the manufactured slab was set to 600℃, 700℃, 750℃, 790℃, 800℃, or 850℃.

[0120] (3) In the hot rolling stage, the slab was reheated to a temperature of 1,220°C, and the finishing rolling temperature was set to 730°C, 760°C, 790°C, 820°C, 850°C, or 880°C, and the coiling temperature was set to 550°C, 650°C, 690°C, 700°C, or 750°C. At this time, the thickness of the hot-rolled plate was rolled to 2.5 mm.

[0121] (4) In the cold rolling stage, the pre-annealed plate is cold-rolled to make a cold-rolled plate with a thickness of 0.5 mm.

[0122] (5) In the cold rolling annealing stage, the cold rolled plate was heated to 850°C and held for 45 seconds. After that, it was cooled.

[0123] (6) A coating layer was formed on the surface of the cold-rolled annealed plate to produce the final product.

[0124] In one embodiment of the present invention, a non-oriented electrical steel sheet manufactured through the above manufacturing method may have a volume fraction of TiC precipitates with an average diameter of 200 nm or less in the final microstructure of 20% or less, and a volume fraction of MnS precipitates with an average diameter of 200 nm or less of 20% or less.

[0125] Fine precipitates with an average diameter of 200 nm or less can act as a factor affecting the magnetic properties of non-oriented electrical steel sheets. More specifically, precipitates with an average diameter of 200 nm or less have a size similar to that of the magnetic domain walls within the grains, and can impede magnetization through a pinning effect during the magnetization of the steel sheet, thereby degrading the magnetic properties of the non-oriented electrical steel sheet. Accordingly, in a non-oriented electrical steel sheet according to one embodiment of the present invention, by controlling the volume fraction of TiC precipitates with an average diameter of 200 nm in the final microstructure to 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less to 20% or less, a non-oriented electrical steel sheet having low iron loss and high magnetic flux density can be provided.

[0126] In one embodiment, the iron loss (W of a non-oriented electrical steel sheet) 15 / 50 ) may be 7.0 W / kg or less. Specifically, the iron loss (W of non-oriented electrical steel) 15 / 50 ) may be 1.0 W / kg or more and 7.0 W / kg or less.

[0127] In one embodiment, in a method for manufacturing a non-oriented electrical steel sheet, the temperature immediately before reheating a slab produced by a continuous casting process may be 800°C or higher. Additionally, in the hot rolling stage, the finish rolling temperature may be 800°C or higher, and the coiling temperature may be less than 600°C. The above-described temperature range is a temperature range for controlling the occurrence of fine precipitates with an average diameter of 200 nm or less. The occurrence of fine precipitates can be effectively suppressed by avoiding a temperature range in which a large amount of fine precipitates with an average diameter of 200 nm or less are precipitated, or by reducing the residence time in the said temperature range.

[0128] measurement method

[0129] (1) Measurement of the volume fraction of the texture

[0130] The volume fraction of the texture can be measured using Electron Backscatter Diffraction (EBSD). More specifically, the {100} and {111} orientation fractions with a deviation angle of 15 degrees or less were measured using EBSD. After mechanical polishing and / or chemical polishing were performed on each specimen, an area of ​​1 cm x 1 cm was measured on the ND plane at the 1 / 4 thickness position using EBSD with an electron beam step size of 10 µm. At this time, the volume fraction was calculated after measuring at least 5,000 grains during the texture measurement.

[0131] (2) Measurement of precipitate size and number

[0132] The number of TiC and MnS precipitates according to their size was measured through Energy Dispersive Spectroscopy (EDS) component analysis. With a minimum EDS resolution of approximately 0.02 µm (e.g., the size of one pixel), the size of the precipitates was classified after measuring a large area of ​​1 cm x 1 cm. In addition, the number of pixels was converted into the number of precipitates to classify the composition and size of the precipitates, and the number of precipitates with a size of 200 nm or less and the number of precipitates with a size greater than 200 nm were measured.

[0133] (3) Measurement of iron loss and magnetic flux density

[0134] Magnetic properties were determined by measuring iron loss and magnetic flux density values ​​in the L direction (parallel to the rolling direction) and C direction (perpendicular to the rolling direction) using a single sheet tester (SST) and calculating the average value. Specifically, for a specimen measuring 60 mm x 60 mm, measurements were taken twice in the L direction and twice in the C direction for a total of four measurements, and the average value was calculated. The specimen was manufactured by punching using a 60 mm x 60 mm punching die. The iron loss was measured at 50 Hz and 1.5 T, and the magnetic flux density was the magnetic flux density at 5000 A / m.

[0135]

[0136] Temperature immediately before specimen reheating, finishing rolling temperature, coiling temperature, TiC volume fraction according to average diameter, MnS volume fraction according to average diameter, iron loss, magnetic flux density, 200 nm or less, 200 nm or less, 200 nm or more, W 15 / 50 (W / kg)B 50(T) Temperature Time Temperature Temperature Time (min) (min) Example 1 8501 208806001 2018.28 1.8 19.28 0.8 4.5 21.77 Example 2 8001 208806001 2019.38 0.7 15.68 4.4 5.8 21.75 Example 3 8001 208506001 2019.78 0.318.28 1.8 6.8 71.75 Example 4 8001 208206001 2012.187 .913.186.93.611.77 Example 5 8001 208806001 2015.784.313.886.23.921.76 Example 6 8001 208805501 2018.381.719.380.74.811.76 Comparative Example 1 7901 208806001 2025.874.223.276.87.281.74 Comparative Example 2 7501 208806001 2044.255.842.3 57.78.68 1.7 Comparative Example 370012088060012031.268.824.275.87.99 1.72 Comparative Example 460012088060012038.261.827.872.28.35 1.72 Comparative Example 580012079060012030.869.226.873.27.86 1.73 Comparative Example 685012088069012028.371.725.874.27. 341.74 Comparative Example 785012088065012027.372.721.378.77.131.74 Comparative Example 880012088075012040.259.832.567.58.441.72 Comparative Example 980012088070012035.264.821.278.88.211.71 Comparative Example 1080012088065012023.876.226.873.27.11.74

[0137] Referring to Table 1, Comparative Examples 1 to 4 fall outside the scope of the present invention, as the temperatures immediately before reheating were 790°C, 750°C, 700°C, and 600°C, respectively. That is, Comparative Examples 1 to 4 have temperatures immediately before reheating of less than 800°C, which falls within the temperature range for the precipitation of TiC and MnS precipitates (fine precipitates) with an average diameter of 200 nm or less. When the temperature immediately before reheating is less than 800°C, the specimen inevitably passes through the temperature range for the precipitation of fine precipitates during the reheating process; consequently, in the case of Comparative Examples 1 to 4, the fine precipitates are excessively precipitated. Therefore, it can be confirmed that in Comparative Examples 1 to 4, the volume fraction of TiC with an average diameter of 200 nm or less exceeds 20%, and the volume fraction of MnS with an average diameter of 200 nm or less also exceeds 20%. Through this, Comparative Examples 1 to 4 [have] iron loss (W 15 / 50 Since the value exceeds 7.0 W / Kg and the magnetic flux density is less than 1.75T, it can be confirmed that the magnetic properties have deteriorated.

[0138] Comparative Example 5 satisfied the scope of the present invention with a temperature of 800°C immediately before reheating, but fell outside the scope of the present invention with a finish rolling temperature of 790°C. That is, Comparative Example 5 has a finish rolling temperature of less than 800°C, which falls within the temperature range for the precipitation of TiC and MnS precipitates (fine precipitates) with an average diameter of 200 nm or less. When the finish rolling temperature is less than 800°C, the specimen passes through the temperature range for the precipitation of fine precipitates during the reheating process; consequently, in the case of Comparative Example 5, the fine precipitates precipitate excessively. Therefore, it can be confirmed that in Comparative Example 5, the volume fraction of TiC with an average diameter of 200 nm or less exceeds 20%, and the volume fraction of MnS with an average diameter of 200 nm or less also exceeds 20%. Through this, Comparative Example 5 [is] iron loss (W 15 / 50 Since the value exceeds 7.0 W / Kg and the magnetic flux density is less than 1.75T, it can be confirmed that the magnetic properties have deteriorated.

[0139] Comparative Examples 6 and 7 satisfied the scope of the present invention with a temperature immediately before reheating of 850°C and a finishing rolling temperature of 880°C, but exceeded the scope of the present invention with coiling temperatures of 690°C and 650°C, respectively. That is, Comparative Examples 6 and 7 include a coiling temperature of 600°C or higher, which is within the precipitation temperature range of TiC and MnS precipitates (fine precipitates) with an average diameter of 200 nm or less.

[0140] In addition, Comparative Examples 8 to 10 satisfied the scope of the present invention with a temperature immediately before reheating of 800°C and a finishing rolling temperature of 880°C, but exceeded the scope of the present invention with coiling temperatures of 750°C, 700°C, and 650°C, respectively. That is, Comparative Examples 8 to 10 include a precipitation temperature range for TiC and MnS precipitates (fine precipitates) with an average diameter of 200 nm or less, with a coiling temperature of 600°C or higher.

[0141] As in Comparative Examples 6 to 10, when the coiling temperature is 600°C or higher, the specimen passes the temperature range for the precipitation of fine precipitates during the reheating process; consequently, in the case of Comparative Examples 6 to 10, the fine precipitates are excessively precipitated. Therefore, it can be confirmed that in Comparative Examples 6 to 10, the volume fraction of TiC with an average diameter of 200 nm or less exceeds 20%, and the volume fraction of MnS with an average diameter of 200 nm or less also exceeds 20%. Through this, Comparative Examples 6 to 10 [have] iron loss (W 15 / 50 Since the value exceeds 7.0 W / Kg and the magnetic flux density is less than 1.75T, it can be confirmed that the magnetic properties have deteriorated.

[0142] Meanwhile, Examples 1 to 6 according to the present invention satisfied the scope of the present invention by having a temperature immediately before reheating of 800°C or 850°C, a finishing rolling temperature of 820°C, 850°C, or 880°C, and a coiling temperature of 550°C or 600°C. That is, Examples 1 to 6 were performed with a temperature immediately before reheating of 800°C or higher, a finishing rolling temperature of 800°C or higher, and a coiling temperature of less than 600°C, thereby avoiding the precipitation temperature range of TiC and MnS precipitates (fine precipitates) with an average diameter of 200 nm or less. Therefore, it can be confirmed that in Examples 1 to 6, the volume fraction of TiC with an average diameter of 200 nm or less is 20% or less, and the volume fraction of MnS with an average diameter of 200 nm or less is 20% or less. Through this, Examples 1 to 6 [satisfy] iron loss (W 15 / 50 It can be confirmed that it has excellent magnetic properties, as the value is less than 7.0 W / Kg and the magnetic flux density is 1.75T or higher.

[0143] As such, the present invention has been described with reference to an embodiment illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and variations of the embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. As a non-oriented electrical steel sheet, In weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities, A non-oriented electrical steel sheet in which the volume fraction of TiC precipitates with an average diameter of 200 nm or less is 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less is 20% or less.

2. In Paragraph 1, The iron loss (W of the above non-oriented electrical steel sheet) 15 / 50 ) is a non-oriented electrical steel sheet with a weight of 7.0W / kg or less.

3. In Paragraph 1, The magnetic flux density (B) of the above non-oriented electrical steel sheet 50 ) is a non-oriented electrical steel sheet with a thickness of 1.75T or more.

4. In Paragraph 1, Non-oriented electrical steel sheet having a final microstructure grain size of 50㎛ to 160㎛.

5. In Paragraph 1, A non-oriented electrical steel sheet having a tensile strength (TS) of 500 MPa or more and a yield strength (YP) of 400 MPa or more.

6. A method for manufacturing non-oriented electrical steel sheets, A continuous casting step for forming a slab comprising, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and other unavoidable impurities; A hot rolling step of manufacturing a hot-rolled plate by reheating the above slab, then hot-rolling and coiling it; A cold rolling step for manufacturing a cold rolled plate by cold rolling the above hot rolled plate; and A cold rolling annealing step for manufacturing a cold rolling annealed plate by annealing the above cold rolling plate; Includes, In the above hot rolling step, the coiling temperature is performed at less than 600℃, and A method for manufacturing a non-oriented electrical steel sheet, wherein the volume fraction of MnS precipitates with an average diameter of 200 nm or less in the final microstructure is 20% or less, 7. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet, wherein the slab temperature is maintained at 800℃ or higher between the continuous casting step and the reheating step.

8. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet, wherein, in the above hot rolling step, the reheating temperature range is 800°C or higher.

9. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet, wherein, in the above hot rolling step, the finishing rolling temperature range is 800℃ or higher.

10. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet in which the volume fraction of TiC precipitates with an average diameter of 200 nm or less in the final microstructure is 20% or less.

11. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet having a final microstructure grain size of 50㎛ to 160㎛.

12. In Paragraph 6, The iron loss (W of the above non-oriented electrical steel sheet) 15 / 50 A method for manufacturing non-oriented electrical steel sheets having a weight of 7.0 W / kg or less.

13. In Paragraph 6, The magnetic flux density (B) of the above non-oriented electrical steel sheet 50 ) is a method for manufacturing non-oriented electrical steel sheets with a thickness of 1.75T or more.

14. In Paragraph 6, A method for manufacturing a non-oriented electrical steel sheet, wherein the tensile strength (TS) of the non-oriented electrical steel sheet is 500 MPa or more and the yield strength (YP) is 400 MPa or more.

15. A motor comprising a motor core, wherein the motor core is, It comprises a non-oriented electrical steel sheet comprising, in weight% (wt%), silicon (Si): 0.1 to 1.6%, aluminum (Al): 0.5% or less (greater than 0), manganese (Mn): 0.2 to 0.4%, carbon (C): 0.0050% or less (greater than 0), sulfur (S): 0.0050% or less (greater than 0), nitrogen (N): 0.0030% or less (greater than 0), titanium (Ti): 0.0050% or less (greater than 0), phosphorus (P): 0.1% or less (greater than 0), and the remainder being iron (Fe) and unavoidable impurities. A motor in which the volume fraction of TiC precipitates with an average diameter of 200 nm or less in the above-mentioned non-oriented electrical steel sheet is 20% or less, and the volume fraction of MnS precipitates with an average diameter of 200 nm or less is 20% or less.

16. In Paragraph 15, The iron loss (W of the above non-oriented electrical steel sheet) 15 / 50 ) is a motor with a weight of 7.0W / kg or less.

17. In Paragraph 15, The magnetic flux density (B) of the above non-oriented electrical steel sheet 50 ) is a motor with a T of 1.75T or more.

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